Messages in this thread |  | | Date | Fri, 5 Feb 2021 20:39:06 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v3 1/2] tpm: fix reference counting for struct tpm_chip |
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On Fri, Feb 05, 2021 at 10:50:02PM +0100, Lino Sanfilippo wrote: > On 05.02.21 at 16:58, Jason Gunthorpe wrote: > eference in the first place). > > > > No, they are all chained together because they are all in the same > > struct: > > > > struct tpm_chip { > > struct device dev; > > struct device devs; > > struct cdev cdev; > > struct cdev cdevs; > > > > dev holds the refcount on memory, when it goes 0 the whole thing is > > kfreed. > > > > The rule is dev's refcount can't go to zero while any other refcount > > is != 0. > > > > For instance devs holds a get on dev that is put back only when devs > > goes to 0: > > > > static void tpm_devs_release(struct device *dev) > > { > > struct tpm_chip *chip = container_of(dev, struct tpm_chip, devs); > > > > /* release the master device reference */ > > put_device(&chip->dev); > > } > > > > Both cdev elements do something similar inside the cdev layer. > > Well this chaining is exactly what does not work nowadays and what the patch is supposed > to fix: currently we dont ever take the extra ref (not even in TPM 2 case, note that > TPM_CHIP_FLAG_TMP2 is never set), so > > - if (chip->flags & TPM_CHIP_FLAG_TPM2) > - get_device(&chip->dev); > + get_device(&chip->dev);
Oh, hah, yes that is busted up. The patch sketch I sent to James is the right way to handle it, feel free to take it up
> and tpm_devs_release() is never called, since there is nothing that ever puts devs, so
Yes, that is a pre-existing memory leak
> The race with only get_device()/putdevice() in tpm_common_open()/tpm_common_release() is:
The refcount handling is busted up and not working the way it is designed, when that is fixed there is no race.
Jason
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